This invention relates to the field of powder metallurgy and more particularly to an improved method for producing rolled stock of a relatively nonductile material with minimum incidence of edge cracking from the rolling operation.
Powder metallurgical techniques are commonly used in forming certain types of materials such as refractory metals, superhard materials and nonductile materials. Powder metallurgy finds important use in the forming of integral parts from intimate mixtures of powdered metals and dispersed nonmetals, such as the silver/cadmium oxide material used in electrical contacts.
The essential steps of a powder metallurgical forming technique are compression of a powder to form a compact (in which the powder particles are "green" or partially bonded) and sintering of the compact (to perfect the "green" or partial bonding) to provide a cohesive integral bonded mass. In many instances, the final product is one having the conformation and dimensions of the sintered compact and the forming technique is thus complete upon sintering. In other instances, however, the sintered compact constitutes an ingot which is further processed by various finishing techniques to provide the final product form. In the case of silver/cadmium oxide contact material, for instance, a sintered silver/cadmium oxide ingot may be rolled to provide a sheet or strip from which contact "buttons" are stamped. Where nonductile or brittle materials are involved, the stresses of rolling frequently induce cracking at the edges of the rolled or partially rolled sheet or strip. As a consequence, rolling is impractical or at least involves production of inordinate amounts of cracked stock which must be scrapped.